If the pads are not joined directly to the rim of the glasses but are fastened to pad levers, the connection between the metal pad lever and the silicon/caoutchouc pad presents difficulties. The pad levers can in the long run pierce the very soft silicon/caoutchouc, even if their front surface has been carefully rounded.
The prevention of rotary movements of the pad relative to the pad lever is even more difficult than is the prevention of axial movements thereof. So far, there does not exist any adhesive which in the long run fulfils the requirements to be met, although adhesive technology is very far advanced.